Patent GB-1328657-A (GB)
Title: Apparatus for processing video singals
IPC: H04N7/084
Filed: 1970-11-06
Abstract: 1328657 Television INTERNATIONAL BUSINESS MACHINES CORP 6 Nov 1970 [24 Nov 1969] 52875/70 Heading H4F A video signal bandwidth compression system utilizes a form of n-fold dot sequential sampling in which a number of picture elements (dots) of the first frame are sampled and passed to a cyclical store, the dots following these first sampled dots are sampled and stored during the second frame and the sampling is continued until after n-frames all the dots have been sampled. The store is then read out at normal speed to reconstitute the video signal. As shown, Fig. 3, during the first frame the picture is sampled as shown so that six samples are taken in every line (one being in the flyback interval). During the second frame the next adjacent dots are sampled on a similar basis, and this is repeated until after the 96th frame every dot has been sampled once. The wide bandwidth video output of a camera (11) is applied to a sample and hold circuit (37) which produces the narrow bandwidth video signal under control of a sync. generator (14). Sampled audio pulses (C) are inserted at the end of each sampled line and sampled audio pulses (C) and slow scan sync. pulses (D) are inserted at the end of each sampled frame, the audio pulses being blacker-than-black and the peaks of the sync. pulses being whiter-thanwhite. The composite narrow bandwidth signals may then be passed through a low pass filter (42) and a transmission system (16), e.g. a telephone line, to a receiver which is provided with a sequential memory (46) in the form of a storage CRT or a magnetic disc arranged to provide a number of storage cells equal to the total number of dots in a frame. The audio pulses are stripped from the signal and the video samples are inserted into the store in such a way that the cells used correspond to the positions of the dots in the original picture. After 96 frames all the store cells are filled and the store is then read out to provide a wide bandwidth signal to which conventional sync. pulses are added, Figs. 1, 2 and 5 to 9 (not shown). Instead of passing the narrow bandwidth signal through a transmission system it may be recorded on a tape recorder. The signal is processed, Figs. 10 and 11 (not shown), by applying it to a pulse width modulator (55) the output of which is differentiated (56) and applied to the recording head (58). When played back the signal comprises half sinusoids (K) which are processed by a peak detector (62), a bi-stable (63) and a pulse width demodulator (64) to reconstitute the video signal. In a modification, Fig. 12 (not shown), the narrow bandwidth video signal is applied to a quantizer (68) to produce a PCM signal which is applied via a data compressor (69) to the transmission medium. At the receiver the signal is applied to a data expander (74) and stored in a digital sequential memory (75) which is read out to produce a wide band PCM video signal which is applied to a digital-to-analogue converter (76) to reconstitute the analogue video signal. Colour pictures can be processed on a frameby-frame or dot sequential basis. In the first method the whole of the red picture is sampled and stored as for monochrome, the green and blue pictures then being similarly sampled and stored in turn. This enables a monochrome camera viewing through coloured filters to be used. In the second method the RGB outputs of a colour camera are sampled in turn so that successive sampled dots are red, green and blue in sequence. In both methods the complete colour picture is stored after 288 (= 3 Î 96) frames have been scanned.